Doing everything right but still lose fish

My 20 gallon H has been set up since August and is cycled. I have a Aquaclear 30 on the tank and even an extra bag of bio-pellets in there. I had a local fish store test my water just after the new year and, I don't remember all the numbers, but he said "I wish everyone's numbers looked this good." I had Petsmart test my water today and she said it is "perfect."

Still, I keep losing at least one fish every 5-6 weeks. The most I've had at one time is 12 (danios, black skirt tetras and mollies/platies). Today, one dead zebra danio and one dead molly. Ironically, my original 3 black skirt tetras that I used to cycle the tank are still alive from last August.

Anyhow I am changing the water (40%) every two weeks (this last time I admit it was 3 weeks because I ran out of water conditioner). Even so, Petsmart lady said my nitrates were not high today (before I did a water change).

Is there anything that could be doing wrong other than water quality??? Or are $1 fish from Petmart just not that hardy???

 

When you get your water tested, do you know if they use the test strips? They are inaccurate and you will be better off buying the liquid API Master Test Kit and doing the tests yourself.

Could you post your stocking list and also the dimensions of your tank? Hexagons hard to stock as they do not have as much surface area as the tank should. This will severely affect how much fish you can actually have.

 

Hello!
I suggest buying the API liquid master test kit. It'll save you a lot of money in the long run as well as let you know your exact parameters. How long have you had the fish? How long has the tank been cycled? Is it planted? Also, have you ever had your tap water tested? Its important to know your ph, gh, and kh. Also ask the store what their ph in their tanks are.
You can try a few things:
-only add 2-3 fish at a time and let your tank adjust for at least a few days
-slowly add some of the ank water into the bag before you add the fish to your tank to get them adjusted to the ph and hardness
-I always net out the fish because the lfs tanks all share water and who knows what else
-is your lfs using strip tests? If so they're probably not accurate
-change your water changes from 40% every 2 weeks to 20% weekly
-make sure your fish are in schools of 6+ (which you might need a bigger tank for) I know black skirts are known to fin nip if not in large schools

Any additional info will help! I've had $1 fish from petsmart for years.

 

You are doing one thing wrong. You are getting other people to test your water.

 

Agreed with Hampalong.
Cave in and get a test kit. You won't regret it

 

Mollies and platties are very, very messy. If you are only changing the water twice a month, nitrates could be sky high due to all the ammonia.
There is no magic weekly number, you must test your water and do changes accordingly. I would invest in a API test kit.

 

Make sure you get a liquid test kit.

 

+1 to the API Master Freshwater Test Kit. You can get it for about ~$25 on Amazon.

 

test kit, do it. I find it so much more accurate than strips.

 

May I ask if you have a heater in your aquarium? One time long ago I use to keep tropical fish in an aquarium, perfectly cycled, and I found that I kept losing fish. Come to find out the temperature kept changing in the tank causing them to get sick and eventually die off. If you don't have a heater in willing to bet that's the case, if you do I suggest what everyone else is saying and getting your own testing kit.

 

Just an observation I thought i'd impart -

If you were doing everything right, you wouldn't be losing fish Thus, something isn't correct. I agree with the API test kit consensus.